Last week delivered one of the most remarkable moments of this most remarkable political season. A major politician defended the conservative movement and the Republican Party from guilt-by-association with a fringe group of racists, anti-Semites and conspiracy theorists who have jumped enthusiastically on the Donald Trump train: the so-called alt-right.

"This is not conservatism as we have known it," the politician said. "This is not Republicanism as we have known it."

That politician was Hillary Clinton, and that's astonishing. Clinton is normally comfortable unjustly condemning conservatism and the GOP for the sins of bigotry and prejudice, not exonerating it. After all, she coined the phrase "vast right-wing conspiracy."

Her husband's administration tried -- unfairly -- to pin the Oklahoma City bombing on conservative critics, specifically radio hosts such as Rush Limbaugh. Less than a decade later, she revived the charge in her book "Living History," tying the bombing to "right-wing radio talk shows and websites [which] intensified the atmosphere of hostility with their rhetoric of intolerance, anger and anti-government paranoia."

Just last year, Clinton was comparing the entire GOP presidential field to "terrorist groups" for their views on abortion.

This history suggests that Clinton's attempt to distinguish the party of Paul Ryan from the alt-right was not the product of high-minded statesmanship, but political calculation. The goal was to demonize Trump so as to make moderate voters feel OK voting for a Democrat.

(Trump is not an alt-righter, but his political inexperience, his anti-establishment persona, and his ignorance of, and hostility to, many basic tenets of conservatism created a golden opportunity for the alt-righters to latch onto his candidacy.)

If I were a down-ballot Democrat, I'd be chagrined. By exonerating the GOP from the stain of the alt-right, Clinton has made it harder for Democratic candidates to tar their opponents with it. What's truly extraordinary, though, is that Clinton is doing work many conservatives won't.

There is a diversity of views among the self-described alt-right. But the one unifying sentiment is racism -- or what they like to call "racialism" or "race realism." In the words of one alt-right leader, Jared Taylor, "the races are not equal and equivalent." On Monday, Taylor asserted on NPR's "The Diane Rehm Show" that racialism -- not religion, economics, etc. -- is the one issue that unites alt-righters.

If you read the writings of leading alt-righters, it is impossible to come to any other conclusion. Some are avowed white supremacists. Some eschew talk of supremacy and instead focus on the need for racial separation to protect "white identity." But one can't talk about the alt-right knowledgeably without recognizing their racism.

And yet that is exactly what some conservatives seem intent on doing. For example, my friend Hugh Hewitt, the influential talk radio host, has been arguing that there is a "narrow" alt-right made up of a "execrable anti-Semitic, white supremacist fringe" but also a "broad alt-right" made up of frustrated tea partiers and others who are simply hostile to the GOP establishment and any form of immigration reform that falls short of mass deportation.

This isn't just wrong, it's madness. The alt-righters are a politically insignificant band. Why claim that a group dedicated to overthrowing conservatism for a white nationalist fantasy is in fact a member of the conservative coalition? Why muddy a distinction the alt-righters are eager to keep clear?

In the 1960s, the fledgling conservative movement was faced with a similar dilemma. The John Birch Society was a paranoid outfit dedicated to the theory that the U.S. government was controlled by communists. It said even Dwight Eisenhower was a Red (to which the conservative political theorist Russell Kirk replied, "Ike's not a Communist, he's a golfer").

William F. Buckley recognized that the Birchers were being used by the liberal media to "anathematize the entire American right wing." At first, his magazine, National Review (where I often hang my hat), tried to argue that the problem was just a narrow "lunatic fringe" of Birchers, and not the rank and file. But very quickly, the editors recognized that the broader movement needed to be denounced and defenestrated.

Buckley grasped something Hewitt and countless lesser pro-Trump pundits do not: Some lines must not be blurred, but illuminated for all to see. Amazingly, Clinton is doing that when actual conservatives have not.